1. Field of the Invention
The present invention relates to an electroacoustic converter, and more particularly is directed to an improvement on an electroacoustic converter such as a loudspeaker or a microphone having a dome-like diaphragm.
2. Related Background Art
In a conventional dome-like loudspeaker, the magnetic circuit is constructed of a center pole, a yoke, a magnet and a top plate. A magnetic gap is formed between the outer wall of the center pole and the inner wall of the top plate. A known diapharagm system is constructed of a unit body of a dome-like diaphragm and a coil bobbin section integrally formed with the diaphragm and having a voice coil wound thereabout, and a curved edge section attached to the unit body. Another is constructed of a unit body of a dome-like diaphragm and an edge section, and a coil bobbin attached to the unit body. In such diaphragm system, the coil bobbin section together with the voice coil is properly inserted in the magnetic gap. Conventionally, a jig shown has been used to precisely define a magnetic gap during an assembly process of a loudspeaker. The jig is formed with a tubular section whose thickness corresponds to the magnetic gap, and the top plate is assembled by covering the tubular section on the center pole. The magnetic circuit elements are coupled together with adhesive agent, and after drying and hardening of the adhesive agent, the jig is removed to complete the magnetic circuit.
Conventional magnetic circuits described above have required a jig for formation of an adequate magnetic gap. In addition, to remove the jig after hardening of the adhesive agent, it is necessary to provide some clearances g between the center pole and the tubular section and between the tubular section and the top plate. As a result, there are associated with some problems that it is difficult to obtain a uniform gap, and that the clearance g must necessarily be incorporated to define the gap distance. This clearance g degrades particularly the performance of a high frequency loudspeaker. Further, use of an adhesive agent for bonding each magnetic circuit element requires a time for drying and hardening, therby resulting in a loss in time during an assembly process.
A dome-like loudspeaker is constructed in such a way that the outer periphery or brim of the edge section extended from the diaphragm is sandwiched between the ring-like edge supporting members which are bonded to the top plate for support of the diaphragm system. With such construction, the leads of the coil wound about the coil bobbin section are drawn to the side of the edge section and sandwiched between the edge supporting members. Generally, a middle- and high-frequency dome-like loudspeaker of this type is small in dimension and has a narrow edge section. Therefore, the leads are carefully guided so as not to contact the edge section or the top plate, and carefully sandwiched so as not to cut or make short-circuited. Such wiring operation of the leads is very difficult and complicated at a limited working space, thus causing a low productivity and a low yield.
In co-pending U.S. application Ser. No. 871,836 filed June 9, 1986, an improvement was proposed. In one example of the improvement, the center pole is chipped off at its shoulder and is mechanically engaged directly with the top plate to define a magnetic air gap. In order to increase the magnetic reluctance at the engaged portions of the center pole and the top plate for the purpose of keeping a high magnetic field in the air gap, the center pole and the top plate are abutted at their corners. In another example, a cylindrical insulator pipe is provided on the outer surface of the center pole. The lower shoulder of the top plate is engaged with the center pole through the pipe to define the magnetic air gap.